# Calculate the magnitude and direction of the torque

• phb1762
In summary, the dipole moment of the HCl molecule can be calculated by assuming point-like ions and using the formula p = Qd, resulting in an answer of 1.6*10^(-29)Cm. The torque exerted on the dipole when subjected to an external electric field can be found using the equation τ = p×E, with the direction of the torque depending on the alignment of the field with the axis of the molecule.
phb1762

## Homework Statement

[/B]
a) (a) Assuming the HCl molecule consists of point-like ions (H+ and Cl) separated by 1.0 * 10^-10m, find the dipole moment of the molecule.
b) Calculate the magnitude and direction of the torque exerted on this dipole if the molecule is subjected to an external electric field of 4.0*10^6 N C^(-1), when the angle between the field direction and the axis of the molecule is 45 degrees.

## Homework Equations

torque = pEsin(theta)

## The Attempt at a Solution

a) Assuming magnitude of charge (Q) on either ion is 1.6*10^(-19)C then using the formula for the dipole moment p = Qd I get an answer of 1.6*10^(-29)Cm.
b) For the second part of the question I'm not too sure how to find the direction of the torque. I have attempted to work out the magnitude using the relevant equation stated above and got 4.5*10^(-23)Nm but I am not too sure about this answer.

P.S I am very sorry for the sloppy writing I understand it may be hard to understand what I mean but I've spent so much time doubting my answer that now I've confused myself! Any help would be appreciated!

Last edited by a moderator:
In order to incorporate direction into your formula
we have
τ = p×E
so if E is 45 degrees counterclockwise of p then τ is counterclockwise
if E is 45 degrees clockwise of p then τ is clockwise

Your problem doesn't state whether it is 45° clockwise or counterclockwise but either way, the dipole will rotate so that p is aligned with E.

## What is torque?

Torque is a measure of the rotational force applied to an object. It is the product of the force applied and the distance from the axis of rotation to the point where the force is applied.

## What is the equation for calculating torque?

The equation for calculating torque is T = F x d x sin θ, where T is torque, F is the force applied, d is the distance from the axis of rotation, and θ is the angle between the force and the lever arm.

## How is torque measured?

Torque is typically measured in units of force times distance, such as Newton-meters (N·m) or foot-pounds (ft·lb).

## What is the difference between magnitude and direction of torque?

The magnitude of torque refers to the strength or size of the torque, while the direction of torque refers to the direction in which the rotational force is applied.

## What factors affect the magnitude and direction of torque?

The magnitude and direction of torque are affected by the magnitude and direction of the applied force, as well as the distance from the axis of rotation to the point where the force is applied and the angle between the force and the lever arm.

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